Regulationof 2-acetyl-1-pyrroline and grain quality in early-season indica fragrant rice by nitrogen and silicon fertilization under different plantationmethods

Fragrant rice has a highmarket value, and it is a popular rice type among consumers owing to itspleasant flavor. Plantation methods,nitrogen (N) fertilizers, and silicon (Si) fertilizers can affect the grainyield and fragrance of fragrant rice. However, the core commercial rice production attributes, namely the headrice yield (HRY) and 2-acetyl-1-pyrroline (2-AP) content of fragrant rice,under various nitrogen and silicon (N-Si) fertilization levels and differentplantation methods remain unknown. Thefield experiment in this study was performed in the early seasons of 2018 and2019 with two popular indica fragrant rice cultivars(Yuxiangyouzhan and Xiangyaxiangzhan). They were grown under six N-Si fertilization treatments (combinations oftwo levels of Si fertilizer, 0 kg Si ha−1 (Si0) and 150 kgSi ha−1 (Si1), and three levels of N fertilizer, 0 kg N ha−1 (N0), 150 kg N ha−1 (N1), and 220 kg N ha−1 (N2)) and three plantation methods (artificial transplanting (AT), mechanicaltransplanting (MT), and mechanical direct-seeding (MD)). The results showed that the N-Sifertilization treatments and all the plantation methods significantly affectedthe HRY and 2-AP content and related parameters of the two different fragrantrice cultivars. Compared with the Si0N0treatment, the N-Si fertilization treatments resulted in higher HRY and 2-APcontents. The rates of brown rice,milled rice, head rice, and chalky rice of the fragrant rice also improved withthe N-Si fertilization treatments. TheN-Si fertilization treatments increased the activities of N metabolism enzymesand the accumulation of N and Si in various parts of the fragrant rice, andaffected their antioxidant response parameters. The key parameters for the HRY and 2-AP content were assessed byredundancy analysis. Furthermore, thestructural equation model revealed that the Si and N accumulation levelsindirectly affected the HRY by affecting the N metabolism enzyme activity, Nuse efficiency, and grain quality of fragrant rice. Moreover, high N and Si accumulation directlypromoted the 2-AP content or affected the antioxidant response parameters andindirectly regulated 2-AP synthesis. Theinteractions of the MT method with the N-Si fertilization treatments varied inthe fragrant rice cultivars in terms of the HRY and 2-AP content, whereas theMD method was beneficial to the 2-AP content in both fragrant rice cultivarsunder the N-Si fertilization treatments.